1. Field of the Invention
The present invention relates to a power amplifier, and more particularly to a power amplifier used in a wireless communication system and is capable of improving the efficiency of an entire output power range and extending an dynamic range without additional switches, by including a drive amplification unit and a power amplification unit, connecting the drive amplification and the power amplification unit to a matching circuit, and a power coupler included in a transmission line transformer such that the drive amplification unit drives the power amplification unit or directly outputs power to an output terminal through the transmission line transformer, that is, the output power of the drive amplification unit is output to a load by switching on/off the power amplification unit and the drive amplification unit.
2. Description of the Related Art
In order to increase efficiency over an entire output power range, a power amplifier for a wireless communication system mainly uses a method of switching on/off a portion of circuits. That is, all circuits are switched on when high power is necessary, and a portion of circuits is switched off when low power is necessary, thereby increasing efficiency in the entire range.
Such a power amplifier is used when a transmitter of a wireless communication system transmits high power through an antenna.
FIG. 1 is a schematic diagram showing the configuration of a general power amplifier having a polar structure, which is a type of wireless communication system.
As shown, in the power amplifier having a polar structure, phase information and envelope information are applied as an input signal, unlike a general linear power amplifier.
The phase information, of which the level is uniform and the phase is changed, is inputted to a radio frequency (RF) input part of a driving amplifier, similar to the general linear power amplifier.
The envelope information is inputted to the power amplifier as a source voltage through a DC-DC converter. The high output power is outputted when the source voltage increases, and the low output power is outputted when the source voltage decreases.
Since the power amplifier having a polar structure can more simplify the structure of a transmitter, compared with the existing linear power amplifier, and a non-linear power amplifier having high efficiency can be used the entire efficiency of the system is improved.
Accordingly, the power amplifier having a polar structure is attracting attention as a next-generation transmitter for a global system for mobile communications (GSM) and an enhanced data GSM environment (EDGE).
Generally, since a RF signal applied to a power amplifier is very weak in driving a power amplification unit, a signal amplified by a primary drive amplification unit and a secondary drive amplification unit drives a power amplification unit to output an RF output signal, as shown in FIG. 1.
Since the general power amplifier is designed such that maximum efficiency is obtained when the output power is at a maximum, the efficiency of the power amplifier deteriorates at a low output power range.
At the low output power range, it is disadvantageous that the level of the signal outputted from the secondary drive amplification unit may become larger than that of the output power of the power amplification unit.
Accordingly, in order to solve such a problem, a plurality of power amplification units is included, as shown in FIG. 2. All the power amplification units are switched on when high output power is outputted and a portion of the power amplification units is switched on when low output power is outputted, such that high efficiency can be obtained in the entire output power range of the power amplifier and the dynamic range of the power amplifier can extend.
However, even in this structure, it is disadvantageous that the level of a signal outputted from the secondary drive amplification unit may become larger than that of the output power of the power amplification units, similar to the general power amplifier shown in FIG. 1.
Accordingly, in order to solve the problem, a power amplifier using switches is suggested as shown in FIG. 3.
In this structure, when middle output power is outputted, the output power of a secondary drive amplification unit is outputted as the output power of the power amplifier by switching off the power amplification unit and switching on a second switch. When low output power is outputted, the output power of a primary drive amplification unit is outputted as the output power of the power amplifier by switching off the power amplification unit and the secondary drive amplification unit, and switching on the first and second switches.
The output power of the primary drive amplification unit or the secondary drive amplification unit is outputted as the final output power of the power amplifier using the switches such that the above-described problem can be solved.
Since the power amplification unit and the secondary drive amplification unit are switched off in the low output power range, it is possible to prevent DC power from being consumed in the power amplification unit and the secondary drive amplification unit to improve the entire efficiency of the power amplifier and to extend the dynamic range.
However, in this case, it is disadvantageous that additional switches are required for outputting the output power of the drive amplification unit as the output power of the power amplifier when the power amplification unit or the secondary drive amplification unit is switched off.
Parasitic resistance components in the additional switches lead to the loss of the output power and the performance deterioration of the power amplifier. In order to prevent the loss of the output power and the performance deterioration of the power amplifier, the sizes of the switches must significantly increase. In this case, the size of the circuit increases and the manufacturing cost of the power amplifier increases.